Ion implantation is a process used in a device manufacturing in which one or more desired species, in a form of ions, are implanted into a target to alter at least one of electrical, optical, chemical, and mechanical property of the target. Depending on the device, the target may be a substrate such as a wafer or a film or other material formed thereon. In integrated circuit (IC) manufacturing, the target may be a silicon wafer. In light emitting diode (LED) manufacturing, the target may be a compound semiconductor substrate. As proper device performance often requires a precise electrical, chemical, or mechanical property, precise ion implantation process is often desired.
The ion implantation system may include an ion source to generate ions of desired species. The ion implantation system may also include a complex series of beam-line components through which the ions generated in the ion source pass. The beam-line components may include, for example, an extraction system, a filter magnet, an acceleration or deceleration column, an analyzer magnet, a rotating mass slit, a scanner, and a corrector magnet. Much like a series of optical lenses that manipulate a light beam, these beam-line components receive the ions, filter, focus, or otherwise manipulate the ions into an ion beam having desired shape, energy, species, angle, and other characteristics. The ion implantation system may also include a number of measurement devices, such as a dose control Faraday cup, a traveling Faraday cup, and a setup Faraday cup to monitor and control the ion beam characteristics.
The substrate located downstream of the beam-line components, may be positioned in the path of the ion beam and exposed to the ion beam. In some ion implantation systems, the positioning of the substrate in the path of the ion beam may be achieved with a substrate scanner (not shown) capable of translating, rotating, and tilting the substrate.
To generate the ions or ion beam of desired species, processing gas with the species is introduced into the ion source and ionized. Generally, the ion source includes indirectly heated cathode (IHC). When powered by a filament disposed near, the cathode in the IHC may emit electrons that ionize the processing gas into ions. The ions of desired species are then extracted from the ion source and directed toward the target via the beam-line components.
The conventional IHC, although adequate, has short lifetime. One cause of the early failure may be due to excessive accumulation of byproducts on the inner surfaces of the ion source. In particular, the processing gas or the ions of the processing gas in the ion source may condense to form the byproduct, and such byproduct may accumulate on the inner wall of the ion source, and the aperture through which the ions are extracted from the ion source (i.e. the extraction aperture). If excessively accumulated on the cathode of IHC, the byproduct may reduce the rate by which the cathode emits the electrons for the ionization. As a result, less than optimum rate of ionization may occur. If excessively accumulated on the extraction aperture, non-uniform ions or ions with undesirable shape may be extracted from the ion source. Consequently, the ion source with excessive material deposited is highly undesirable.
To remove the byproduct, the ion source may have to be periodically cleaned or replaced with another ion source without the byproduct. The process by which the ion source is replaced or cleaned, however, may require powering down the entire ion implantation system, during which the ion implantation system cannot be utilized. Additional time to power up and tune the ion implanter is also needed before the ion implantation system can be used. As a result, performance degradation and short lifetime of the ion source greatly reduces the productivity of the ion implantation system.
In view of the foregoing, it would be desirable to provide a technique for improving the performance and extending the lifetime of an ion source to overcome the above-described inadequacies and shortcomings.